This invention relates to seals for oil or gas wellheads, and more particularly to metal seals for providing an extreme temperature, high pressure metal-to-metal barrier between an un-machined or otherwise rough outer surface of a well casing and a surrounding wellhead component.
Although non-metallic packoffs that are used as seals between a well casing and a wellhead housing are known to be satisfactory for a variety of conditions, such packoffs fail to provide the desired sealing functions when subjected to extreme high temperatures and pressures because of cold flowing, extrusion and/or a phenomenon known in the industry as "explosive decompression." As well depth increases, and as greater pressures and temperatures are encountered, the need for better and more reliable wellhead packoffs and seals also increases.